Dredge cutting forces produced by the movement of the cutterhead through the sediment have been measured with the laboratory dredge carriage located at the Haynes Coastal Engineering Laboratory. The sediment bed that was used for the dredging test was considered to be relatively smooth and the sediment used was sand with a d50=0.27 mm. Forces on the dredge carriage were measured using five 13.3 kN (3000 lb) one directional load cells placed on the dredge ladder in various places so the transmitted cutting forces could be obtained. The objectives for this study are to determine the vertical, horizontal, and axial forces that are produced by the cutterhead while testing. So, to find these cutter forces, a static analysis was performed on the carriage by applying static loads to the cutterhead in the vertical, horizontal, and axial directions, and for each load that was applied, readings were recorded for all five of the load cells. Then, static equilibrium equations were developed for the dredge carriage ladder to determine loads in the five load cells. Also, equilibrium equations can be applied to a dredging test to find the cutterhead forces by taking the measured data from the five load cells and applying the known forces to the equations, and the cutterhead forces can be determined. These static equilibrium equations have been confirmed by using a program called SolidWorks, which is modeling software that can be used to do static finite element analysis of structural systems to determine stresses, displacement, and pin and bolt forces. Data that were gathered from the experimental procedure and the theoretical calculations show that the force on the dredge cutterhead can be determined. However, the results from the static equilibrium calculations and the results from the SolidWorks program were compared to the experiment procedure results, and from the comparison the procedure results show irregularities when a force of approximately 0.889 kN (200 lb) or above is applied to the cutterhead in a north, south, west, or east orientation. The SolidWorks program was used to determine the results for displacements of the dredge carriage ladder system, which showed that large displacements were occurring at the location of the cutterhead, and when the cutterhead displaces it means that the carriage ladder is also moving, which causes false readings in the five load cells. From this analysis it was determined that a sixth force transducer was needed to produce more resistance on the ladder; and the cell #1 location needed to be redesigned to make the ladder system as rigid as possible and able to produce good testing results. The SolidWorks program was used to determine the best location where the sixth force transducer would give the best results, and this location was determined to be on the lower south-west corner oriented in the direction east to west. The static equilibrium equations were rewritten to include the new redesigned cell #1 location and the new location of the sixth load cell. From the new system of equations, forces on the cutterhead can be determined for future dredging studies conducted with the dredge carriage. Finally, the forces on the laboratory cuttersuction dredge model cutterhead were scaled up to the prototype 61 cm (24 in) cuttersuction dredge. These scaled up cutting forces on the dredge cutterhead can be utilized in the design of the swing winches, swing cable size, ladder supports, and ladder.

Herein, we study the contact damage performance of two armour ceramics, alumina and silicon carbide, with varying microstructures and one particle-reinforced ceramic nanocomposite, alumina/silicon carbide, in an attempt to understand the microstructural mechanisms that affect plasticity and cracking under quasi-static and dynamic conditions. Quasi-static contact damage was imitated using Vickers indentation over a varying load regime. Numerical analysis of the indentation size effect, performed using the proportional specimen resistance model, allowed the contributions of plastic deformation and cracking to be separated into two individual values. In all three samples, higher levels of surface energy were found to correlate with increased amounts of cracking per unit area of indentation impression. Analytical modelling of crack initiation during Vickers indentation together with quantitative measurements of surface flaw populations revealed that such an increase in cracking damage was the result of higher densities of larger flaws. The hardness of the monolithic ceramics was found vary based on grain size and porosity levels, a smaller average grain size and lower porosity levels resulting in higher hardness values. In the nanocomposite materials, hardening was found to occur with further additions of silicon carbide nanoparticles. Such an effect has been attributed to the increased dislocation densities, as measured using Cr3+/Al2O3 fluorescence spectroscopy, and the impedance of dislocation movement within the lattice due to the presence of silicon carbide nanoparticles. In order to simulate dynamic contact damage, a low velocity, scaled-down drop-weight test was designed and developed. The dynamic contact damage resistance was determined based on the depth of penetration of a blunt indenter. In the monolithic ceramics, the indenter penetration was found to be shallower in materials of higher hardness. However, the nanocomposite materials displayed an opposing trend, the indenter penetration becoming deeper in the samples of higher hardness. The macro-scale fracture patterns produced during drop-weight impacts were seen to vary based on flaw populations and indenter penetration. In certain microstructures, extensive micro-cracking was also observed.

No description available.

No description available.

Plane ring meshes can be produced in large dimensions for various applications, for example, in architecture or protective systems. The numerical simulation of all individual rings of ring meshes is very costly, which is why methods to abstract the structure have been sought in the past. In this paper, a method for determining the strain parameters of a representative ring mesh section under in-plane tensile loads is presented. Methods of rigid body analysis and representative volume elements with periodic boundary conditions are used. Green Lagrangian strain tensors are determined for both an exemplary representative ring mesh section under different tensile load cases and an experimental ring mesh under one load case. The comparison of the Green Lagrangian strain tensors of the ring meshes between numerical simulations and experiments shows a very good agreement.

Several studies were undertaken by various investigators during the last five decades to better understand the engineering behaviour of unsaturated soils. These studies are justified as more than 33% of soils worldwide are found in either arid or semi-arid regions with evaporation losses exceeding water infiltration. Due to this reason, the natural ground water table in these regions is typically at a greater depth and the soil above it is in a state of unsaturated conditions. Foundations of structures such as the housing subdivisions, multi-storey buildings, bridges, retaining walls, silos, and other infrastructure constructed in these regions in sandy soils are usually built within the unsaturated zone (i.e., vadose zone). Limited studies are reported in the literature to understand the influence of capillary stresses (i.e., matric suction) on the bearing capacity, settlement and liquefaction potential of unsaturated sands. The influence of matric suction in the unsaturated zone of the sandy soils is ignored while estimating or evaluating bearing capacity, settlement and liquefaction resistance in conventional engineering practice. The focus of the research presented in the thesis has been directed towards better understanding of these aspects and providing rational and yet simple tools for the design of shallow foundations (i.e., footings) in sands under both static and dynamic loading conditions. Terzaghi (1943) or Meyerhof (1951) equations for bearing capacity and Schmertmann et al. (1978) equation for settlement are routinely used by practicing engineers for sandy soils based on saturated soil properties. The assumption of saturated conditions leads to conservative estimates for bearing capacity; however, neglecting the influence of capillary stresses contributes to unreliable estimates of settlement or differential settlement of footings in unsaturated sands. There are no studies reported in the literature on how capillary stresses influence liquefaction, bearing capacity and settlement behavior in earthquake prone regions under dynamic loading conditions. An extensive experimental program has been undertaken to study these parameters using several specially designed and constructed equipment at the University of Ottawa. The influence of matric suction, confinement and dilation on the bearing capacity of model footings in unsaturated sand was determined using the University of Ottawa Bearing Capacity Equipment (UOBCE-2011). Several series of plate load tests (PLTs) were carried out on a sandy soil both under saturated and unsaturated conditions. Based on these studies, a semi-empirical equation has been proposed for estimating the variation of bearing capacity with respect to matric suction. The saturated shear strength parameters and the soil water characteristic curve (SWCC) are required for using the proposed equation. This equation is consistent with the bearing capacity equation originally proposed by Terzaghi (1943) and later extended by Meyerhof (1951) for saturated soils. Chapter 2 provides the details of these studies. The cone penetration test (CPT) is conventionally used for estimating the bearing capacity of foundations because it is simple and quick, while providing continuous records with depth. In this research program, a cone penetrometer was specially designed to investigate the influence of matric suction on the cone resistance in a controlled laboratory environment. Several series of CPTs were conducted in sand under both saturated and unsaturated conditions. Simple correlations were proposed from CPTs data to relate the bearing capacity of shallow foundations to cone resistance in saturated and unsaturated sands. The details of these studies are presented and summarized in Chapter 3. Standard penetration tests (SPTs) and PLTs were conducted in-situ sand deposit at Carp region in Ottawa under both saturated and unsaturated conditions. The test results from the SPTs and PLTs at Carp were used along with other data from the literature for developing correlations for estimating the bearing capacity of both saturated and unsaturated sands. The proposed SPT-CPT-based technique is simple and reliable for estimation of the bearing capacity of footings in sands. Chapter 4 summarizes the details of these investigations. Empirical relationships were proposed using the CPTs data to estimate the modulus of elasticity of sands for settlement estimation of footings in both saturated and unsaturated sands. This was achieved by modifying the Schmertmann et al. (1978) equation, which is conventionally used for settlement estimations in practice. Comparisons are provided between the three CPT-based methods that are commonly used for settlement estimations in practice and the proposed method for seven large scale footings in sandy soils. The results of the comparisons show that the proposed method provides better estimations for both saturated and unsaturated sands. Chapter 5 summarizes the details of these studies. A Flexible Laminar Shear Box (FLSB of 800-mm3 in size) was specially designed and constructed to simulate and better understand the behaviour of model surface footing under seismic loads taking account of the influence of matric suction in an unsaturated sandy soil. The main purpose of using the FLSB is to simulate realistic in-situ soils behaviour during earthquake ground shaking. The FLSB test setup with model footing was placed on unidirectional 1-g shake table (aluminum platform of 1000-mm2 in size) during testing. The resistance of unsaturated sand to deformations and liquefaction under seismic loads was investigated. The results of the study show that matric suction offers significant resistance to liquefaction and settlement of footings in sand. Details of the equipment setup, test procedure and results of this study are presented in Chapter 6. Simple techniques are provided in this thesis for estimating the bearing capacity and settlement behaviour of sandy soils taking account of the influence of capillary stresses (i.e., matric suction). These techniques are consistent with the methods used in conventional geotechnical engineering practice. The studies show that even low values of capillary stresses (i.e., 0 to 5 kPa) increases the bearing capacity by two to four folds, and the settlement of footings not only decreases significantly but also offers resistance to liquefaction in sands. These studies are promising and encouraging to use ground improvement techniques; such as capillary barrier techniques to maintain capillary stresses within the zone of influence below shallow foundations. Such techniques, not only contribute to the increase of bearing capacity, they reduce settlement and alleviate problems associated with earthquake effects in sandy soils.

Several studies were undertaken by various investigators during the last five decades to better understand the engineering behaviour of unsaturated soils. These studies are justified as more than 33% of soils worldwide are found in either arid or semi-arid regions with evaporation losses exceeding water infiltration. Due to this reason, the natural ground water table in these regions is typically at a greater depth and the soil above it is in a state of unsaturated conditions. Foundations of structures such as the housing subdivisions, multi-storey buildings, bridges, retaining walls, silos, and other infrastructure constructed in these regions in sandy soils are usually built within the unsaturated zone (i.e., vadose zone). Limited studies are reported in the literature to understand the influence of capillary stresses (i.e., matric suction) on the bearing capacity, settlement and liquefaction potential of unsaturated sands. The influence of matric suction in the unsaturated zone of the sandy soils is ignored while estimating or evaluating bearing capacity, settlement and liquefaction resistance in conventional engineering practice. The focus of the research presented in the thesis has been directed towards better understanding of these aspects and providing rational and yet simple tools for the design of shallow foundations (i.e., footings) in sands under both static and dynamic loading conditions. Terzaghi (1943) or Meyerhof (1951) equations for bearing capacity and Schmertmann et al. (1978) equation for settlement are routinely used by practicing engineers for sandy soils based on saturated soil properties. The assumption of saturated conditions leads to conservative estimates for bearing capacity; however, neglecting the influence of capillary stresses contributes to unreliable estimates of settlement or differential settlement of footings in unsaturated sands. There are no studies reported in the literature on how capillary stresses influence liquefaction, bearing capacity and settlement behavior in earthquake prone regions under dynamic loading conditions. An extensive experimental program has been undertaken to study these parameters using several specially designed and constructed equipment at the University of Ottawa. The influence of matric suction, confinement and dilation on the bearing capacity of model footings in unsaturated sand was determined using the University of Ottawa Bearing Capacity Equipment (UOBCE-2011). Several series of plate load tests (PLTs) were carried out on a sandy soil both under saturated and unsaturated conditions. Based on these studies, a semi-empirical equation has been proposed for estimating the variation of bearing capacity with respect to matric suction. The saturated shear strength parameters and the soil water characteristic curve (SWCC) are required for using the proposed equation. This equation is consistent with the bearing capacity equation originally proposed by Terzaghi (1943) and later extended by Meyerhof (1951) for saturated soils. Chapter 2 provides the details of these studies. The cone penetration test (CPT) is conventionally used for estimating the bearing capacity of foundations because it is simple and quick, while providing continuous records with depth. In this research program, a cone penetrometer was specially designed to investigate the influence of matric suction on the cone resistance in a controlled laboratory environment. Several series of CPTs were conducted in sand under both saturated and unsaturated conditions. Simple correlations were proposed from CPTs data to relate the bearing capacity of shallow foundations to cone resistance in saturated and unsaturated sands. The details of these studies are presented and summarized in Chapter 3. Standard penetration tests (SPTs) and PLTs were conducted in-situ sand deposit at Carp region in Ottawa under both saturated and unsaturated conditions. The test results from the SPTs and PLTs at Carp were used along with other data from the literature for developing correlations for estimating the bearing capacity of both saturated and unsaturated sands. The proposed SPT-CPT-based technique is simple and reliable for estimation of the bearing capacity of footings in sands. Chapter 4 summarizes the details of these investigations. Empirical relationships were proposed using the CPTs data to estimate the modulus of elasticity of sands for settlement estimation of footings in both saturated and unsaturated sands. This was achieved by modifying the Schmertmann et al. (1978) equation, which is conventionally used for settlement estimations in practice. Comparisons are provided between the three CPT-based methods that are commonly used for settlement estimations in practice and the proposed method for seven large scale footings in sandy soils. The results of the comparisons show that the proposed method provides better estimations for both saturated and unsaturated sands. Chapter 5 summarizes the details of these studies. A Flexible Laminar Shear Box (FLSB of 800-mm3 in size) was specially designed and constructed to simulate and better understand the behaviour of model surface footing under seismic loads taking account of the influence of matric suction in an unsaturated sandy soil. The main purpose of using the FLSB is to simulate realistic in-situ soils behaviour during earthquake ground shaking. The FLSB test setup with model footing was placed on unidirectional 1-g shake table (aluminum platform of 1000-mm2 in size) during testing. The resistance of unsaturated sand to deformations and liquefaction under seismic loads was investigated. The results of the study show that matric suction offers significant resistance to liquefaction and settlement of footings in sand. Details of the equipment setup, test procedure and results of this study are presented in Chapter 6. Simple techniques are provided in this thesis for estimating the bearing capacity and settlement behaviour of sandy soils taking account of the influence of capillary stresses (i.e., matric suction). These techniques are consistent with the methods used in conventional geotechnical engineering practice. The studies show that even low values of capillary stresses (i.e., 0 to 5 kPa) increases the bearing capacity by two to four folds, and the settlement of footings not only decreases significantly but also offers resistance to liquefaction in sands. These studies are promising and encouraging to use ground improvement techniques; such as capillary barrier techniques to maintain capillary stresses within the zone of influence below shallow foundations. Such techniques, not only contribute to the increase of bearing capacity, they reduce settlement and alleviate problems associated with earthquake effects in sandy soils.

Fiber reinforced polymer composite laminates make up more than 50% of modern aircrafts. Such composite laminates are exposed to various environmental and in-service thermo-mechanical load conditions. Transverse/intralaminar cracking is usually the first form of damage appears in a composite laminate and they tend to increase in number during the service life. The growth in number of these cracks significantly degrades the thermo-elastic properties of the composite laminate and eventually leads to final failure. Thus, it is important to predict the crack density (number of cracks per unit length) growth in both non-interactive crack density region and interactive crack density region and its effect in thermo-elastic properties degradation. Non-interactive crack density region is the region where the cracks are far apart and stress perturbation between cracks do not overlap. Interactive crack density region is where the cracks are close to each other and stress perturbation between cracks overlaps and affects the formation of new cracks. In this study, transverse cracks in thick Glass Fiber Epoxy (GF/EP) cross-ply composite laminates under quasi-static tensile loading and tension-tension fatigue loading have been analyzed and predicted. In the first paper attached here, increase in number of transverse cracks in GF/EP cross-ply laminates under quasi-static tensile loading at room temperature (RT) are analyzed using 2 material systems. The failure stress distribution in 90° plies of the laminates is defined by Weibull distribution and the Weibull parameters are determined from crack density versus applied thermo-mechanical transverse stress in 90° layer (σTCLT) data points within the non-interactive crack density region. The crack density growth is then predicted versus the σTCLT and applied mechanical strain in the laminate from the determined Weibull parameters using Monte Carlo method and the stress distribution models between adjacent cracks. The predicted results using the novel stress distribution model introduced here were in good agreement with the non-interactive and interactive crack density regions of test results. The importance of using the Monte Carlo method and novel stress distribution model to predict the whole crack density region have been emphasized in the article, in addition to that it also redefined the interval of non-interactive crack density region.  The second paper expands the concept from the first paper, to address the tension-tension fatigue loading at RT. It deals with the crack density analysis and prediction in [0/90]s GF/EP laminate under fatigue loading at RT. The fatigue tests were performed at 3 maximum stress levels. Here the Weibull parameters were determined from the data points within the non-interactive crack density region in quasi-static and fatigue loading. From the determined Weibull parameters of each stress level and using Monte Carlo method and the novel stress distribution model, the crack density versus the number of fatigue cycles were predicted and in good agreement with the fatigue test results at the respective stress level. The intention here was to use Weibull parameters of one stress level to predict crack density at arbitrary stress levels. Based on it, the predicted results were not sufficiently good and suggested to revisit the Weibull parameter determination by performing fatigue tests at two stress levels.  In the attached paper 3, new methodology on crack density growth simulation and Weibull parameter determination in tension-tension fatigue loading has been developed. In the newly developed methodology, in detailed fatigue tests are performed at one maximum stress level to obtain all data points and at higher stress level to obtain one data point that is a crack density data point at certain number of cycles to determine Weibull parameters. Using the determined Weibull parameters from non-interactive crack density region, the whole crack density region was successfully predicted for other stress levels.

Wooden objects have been widely used in the history of humanity and play an important role in our cultural heritage. The preservation of such objects is of great importance and can be a challenging task. This thesis investigates the static and time-dependent mechanical behaviour of archaeological oak wood from the Vasa warship. Characterisation of mechanical properties is necessary for the formulation of a numerical model to design an improved support structure. The ship was impregnated with polyethylene glycol (PEG) for dimensional stabilisation. All elastic engineering constants of the Vasa oak have been identified and compared with those of recent oak by means of the static and dynamic testing. The experiments were done on samples with cubic geometry, which allowed obtaining all elastic constants from a single sample. The usage of cubic samples with orthotropic mechanical properties during compressive experiments was validated with finite-element simulations. The Young's moduli of the Vasa oak in all orthotropic directions were smaller than those for the recent oak. The shear moduli of Vasa oak was determined and verified with the resonant ultrasound spectroscopy. The time-dependent mechanical behaviour of the Vasa oak has been studied. Creep studies were performed in uniaxial compression on the cubic samples in all orthotropic directions. The samples loaded in the longitudinal direction were subjected to different stress levels. A stress level below 15% of the yield stress in the longitudinal direction did not result in non-linear creep with increasing creep rates within the time frame of the tests. The results of the studies in radial and tangential directions showed that creep was dominated by the effect of annual fluctuations in relative humidity and temperature. The weight changes based on annual fluctuations of relative humidity were measured for Vasa oak and recent oak. The Vasa oak showed higher variations due to an increased hygroscopicity which is the result of the impregnation with PEG. In conceiving a full-scale finite-element model of Vasa ship, not only the stress-strain relations of the material but also those of the structural joints are needed. Since the in-situ measurement of joints is not an option, a replica of a section of the ship hull was built and tested mechanically. The load-induced displacements were measured using 3D laser scanning which proved to have advantages to conventional point displacement measurements. The mechanical characteristics of the Vasa oak and joint information presented in this work can be used as input for a finite-element model of the Vasa ship for simulation of static and time-dependent behaviour on a larger scale. / Stötta Vasa

Although branch plate connections with circular hollow section (CHS) members are simple to fabricate and cost-effective, they are generally very flexible under low load application resulting in the limit states design resistance being governed by an imposed deformation limit. Restricting the ultimate capacity of a branch plate connection by a deformation limit results in the inherent strength of the CHS member being under-utilized, highlighting the need to develop connection stiffening methods. Two methods to stiffen branch plate-to-CHS connections are examined: a through plate connection and a grout-filled CHS branch plate connection. Further, the current design guidelines of various plate-to-CHS connection types are reexamined including the effect of chord axial stress and chord length on connection behaviour. Finally, the behaviour of connections with non-orthogonal or skew plate orientation, which has not previously been examined, was studied in depth.The behaviour of these uniplanar connection types under quasi-static axial loading was studied through 16 large-scale laboratory experiments and 682 numerical finite element analyses, as well as an extensive review of all previous international experimental and numerical findings. The extensive study formed the basis for a complete set of proposed design guidelines and provided insight into plate-to-CHS connection behaviour. For all plate-to-CHS connection types, the plate thickness is shown to effect connection capacity, though previously this was thought not to have significant impact on connection behaviour. The existing ideology of using the same design recommendations for tension- and compression-loaded connections, which was developed from compression results, under-utilizes an inherent increase in capacity provided by a connection primarily loaded in tension. As such, the recommended design guidelines split the two load senses into separate expressions that reflect the difference in behaviour. Stiffened through plate connection behaviour was determined to be the summation of branch plate behaviour in compression and tension, leading to a significant increase in capacity and identical behaviour regardless of branch load sense. The skewed branch plate connection behaviour was found to relate directly to the established behaviour of longitudinal and transverse plate connections. A design function was developed that interpolates the capacities of intermediate angles by using the proposed design recommendations of the two extreme connection types. Finally, the examination of chord axial stress and chord length for plate-to-CHS connections yielded results similar to previous international studies on CHS-to-CHS connections. The effect of chord length, however, has wide-reaching implications as to how experimental and numerical FE research programs are developed.